Salt the cucumber, leave to absorb in a sieve for approx. 30 mins., then press out all the liquid. Mix the cucumber, yoghurt and lemon juice, cover and chill. Puree the chickpeas and garlic with the oil and lemon juice, season. Roughly mix the tzatziki into the hummus, spread on a platter.
Heat the oil in a non-stick frying pan. Add the potatoes, fry for approx. 5 mins., reduce the heat, cover and continue to cook for approx. 20 mins., turning occasionally. Remove the lid, salt the potatoes, cook for a further 5 mins. Remove the potatoes, keep warm.
Combine the oil, lemon zest and oregano, thread the lamb and olives on to the skewers, brush with the marinade, season with salt. Grill the skewers covered over/on a medium heat (approx. 200 °C for approx. 12 mins., turning occasionally. Arrange the skewers and potatoes on top of the tzatziki hummus, garnish with the reserved oregano.